Mirror KB Articles
about horses & horse care

by Kim and Kari Baker

Mirror KB Equine Article Series

Equine Drug TherapyPart 2Article and Photos by Kim and Kari Baker

"The age of the horse is often a factor in how a drug will be
absorbed. The drug dosage in adults
and foals is ascertained by weight, but since young foals may not
metabolize or eliminate drugs as effectively, the dosage of certain
drugs is often slightly reduced. A decrease in drug dosage might also be
called for in the geriatric horse due to the slowing of body
functions," says Schaumberg.

Another factor that can affect the horse's responsiveness to a drug is
the condition of the digestive system. When administering an oral drug,
the extent of absorption will differ depending on conditions in the gut.

"The pH (a measure of acidity) of the stomach acid varies within a
normal range in a horse," explains Schaumberg."Diet, hormonal influences on stomach
mucosa, stress, and
many other factors affect the stomach pH. A one-point change in pH can
dramatically influence the stomach's absorption of a drug."

An example of this might be if the horse suffers from diarrhea. The
effectiveness of the drug will generally be decreased due to the rapid
rate of passage through the gut. On the flip side, constipation might
enhance the absorption of the drug due to slowed movement through the
intestinal tract.

"Drugs are also excreted through the kidneys, as well as through
sweat or exhalation, and can be excreted whole or broken down as
metabolites," adds Schaumberg. "For instance, urinary
excretion is also affected by pH. Acidic urine increases the excretion
of basic drugs, while a more alkaline urine readily excretes drugs with
a low pH."Wilson,
adds, "Many drugs are metabolized by the liver and eliminated
either in the bile or re-circulated through the kidneys to be eliminated
in urine."Other
factors that must be taken into account when selecting a drug and
deciding on the proper dosage for that particular horse include
determining the horse's temperament, general health, body lean to fat
ratio, and whether the drug is safe for a pregnant mare (if that's the
intended use).

"The bottom line is, you should know the range of dosage in
accordance with the horse's weight and age and adjust up and down
according to the factors that you are aware of," advises Schaumberg.
"This is why doing a blood work-up to establish cholesterol,
triglyceride, or albumin (proteins that are soluble in water) levels
allows the veterinarian to make a more informed decision. "Wilson also stresses the importance in the evaluation of both the
kidney and liver functions.

While
many drugs can be safely used together, it can be potentially dangerous
to the horse to administer more than one drug. For this reason, when
administering any drug, it's very important to understand how it will
affect the horse in the presence of an additional drug. "There are
literally hundreds of drug interactions," says Schaumberg. "An
antibiotic like tetracycline is bacteriostatic (slows growth) will
interfere with an antibiotic like penicillin that is bactericidal (kills
only growing bacteria). Drugs, like Lasix (a diuretic also known as
Salix), will cause some drugs that are excreted by the kidneys to be
excreted faster."

Have
diligent records of drug usage, and keep these records handy so they can
be referenced prior to administering any medication. If there is a
question of drug compatibility, you should consult your veterinarian
before administering a second drug. This includes supplements and
dewormers. For example, any tranquilizer in the promazine group cannot
be used safely if a horse has recently been dewormed with a piperazine,
phenothiazine or organophosphate product, as these will significantly
increase the likelihood of toxicity.

With
only a few exceptions, drug dosage is presented as a weight unit of the
drug for each weight unit of the horse. Keep in mind formulations of
like drugs are not always equal. They can vary in the concentration of
active and inactive ingredients depending on the manufacturer of the
drug. In particular, concentrations vary in injectables, such as the
vitamin B complexes and various antibacterial agents.

When
medicating a horse, the owner must always fulfill his/her
responsibilities. This means you must attempt to understand the function
of the chemicals you plan to use, how each drug works, its intended use,
and what it will or will not do.

Medications should never be used for a
purpose that differs from what they are designated to do unless
prescribed by a veterinarian. At no time should a drug be used in an
indiscriminate manner, such as on a horse other than the horse that the
drug was the originally prescribed for. Neither should a drug
specifically produced for horse be used on other animals or humans.

If
properly prescribed and administered, drugs establish a valued defense
in the treatment of many illnesses and injuries that affect the horse.

Safe
Management of Drugs

•
Consult your veterinarian if you are unsure of a particular health
concern and the appropriate treatment for your horse.

•
Drugs, whatever the type, should be stored far out of reach of children,
away from exposure to direct sunlight, and within the appropriate
temperature range suggested by the manufacturer.

•
Always note the expiration date on drug labels and avoid using any
product that has expired or appears to have discolored. Even if the
expiration date is okay, if it looks odd to you in any way don't use it!

•
Always dispense drugs according to the manufacturer's or veterinarian's
directions, whether topically, orally, or by injection (i.e.,
intramuscular, subcutaneous, etc.). Some drugs can only be given
intramuscularly, such as procaine penicillin and most vaccines. Others,
like the injectable form of phenylbutazone (Bute), are very irritating
to the muscles and should only be given through an intravenous
injection.

•
Know how to administer drugs properly. Get help or advice from your
veterinarian if you are unsure of the proper sites and methods used when
administering an injectable medication.

•
Stick to proper hygiene when giving an injectable medication--avoid
contamination of the bottle. Passing dirty needles through a dirty top
will introduce bacteria that can cause serious infections. Appropriate
cleansing of the injection site is also important to help prevent
contamination of the underlying tissues.

•
Never mix products unless specifically recommended by the manufacturer.

•
Do not save partially used vaccine vials for later use.

•
When using a multiple-dose vial, never enter the container with an
unsterile needle.

•
Properly disinfect all re-usable equipment, specifically syringes,
needles, etc. Strong chemical disinfectants that might be inadvertently
left remaining in a syringe can destroy both live and modified live
biologicals. For this reason, it's best to boil equipment in distilled
water for 20 minutes rather than sterilizing in alcohol or other
disinfectants.

•
Dispose of used containers, vials, needles, and syringes properly. Do
not leave them where they will become a hazard to man or animal. (Beware
of needles dropping in bedding!)

•
Along with the product's caution statement for appropriate handling,
read the directions for the drug's proper use and method of
administration, then follow them exactly.

• Take the time to learn about the possible side effects of each drug
you intend to use and what emergency steps you must take should your
horse experience a reaction to the drug.

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